Energy issues are the serious concern of all countries in the world. Solar energy is the best alternative energy for mankind in the future, how to convert solar energy into electrical power is a hotspot in research. In recent years, conjugated polymer thin film organic solar cells got a substantial development, due to its advantages of low cost, light weight, simple fabrication process, can be prepared into flexible devices, etc. In addition, many kinds of organic materials can be used as the material of the thin film organic solar cells, and strong in design, it is hopeful to improve the performance of the organic solar cells through the design and optimization of materials.
By well design and optimization of the material, it can regulate the absorption spectrum, HOMO level, LUMO level, and transmission properties of conjugated polymers, and these properties play a very important role in spectrum absorption, carrier generation, collection of carriers on the electrode, and current yielding. In the past decade, conjugated polymers with the receptor system has obtained rapid development, it is proved by continuous research that, the receptor system can effectively regulate HOMO and LUMO levels and band gap of the organic semiconductor.
For recent years, the receptor system of small molecules which containing diketopyrrolo[3,4-c]pyrrole (DPP) unit (Walker B., Tomayo A. B., Nguyen T. Q., et al. Adv. Funct. Mater., 2009, 19, 3063), conjugated polymer (Allard N., R. B. Ai″ch, Leclerc M, et al. Macromolecules, 2010, 43, 2328) are frequency reported. the energy conversion efficiency of polymers/PCBM based on DPP and small molecule solar energy cells based on DPP are as high as 4.7% and 4.4%. Both isoindigo and DPP contains central symmetric pyrrolidone nucleus, alkylation reaction on N atom becomes very easy, thus materials containing isoindigo unit is a promising high performance organic solar cells materials. However, materials containing isoindigo unit has few reports so far, which greatly limits its scope of application.